1. Field of the Invention
Development of a permanent base on the Moon's surface may lead to human and animal colonization, which will require a plentiful supply of both oxygen gas for respiration and refined metals for structural materials. New technical strategies must be developed for the generation of useful chemical species from lunar materials directly on the Moon's surface due to the prohibitive costs associated with the transportation of necessary materials from Earth.
The present invention relates to a process and apparatus for electrochemical separation of alkali oxides to simultaneously generate oxygen gas and liquid alkali metals in a high temperature electrolytic cell. The process and apparatus of the present invention would be particularly applicable under lunar conditions and liquid alkali metal removed from the electrolytic cell may be utilized in the direct thermochemical refining of lunar metal oxide ores. A preferred process system of the present invention provides electrochemical separation of Li.sub.2 O in a high temperature electrolytic cell to simultaneously generate liquid lithium and oxygen gas, followed by the chemical oxidation of liquid lithium by reaction with lunar metal oxide ores producing reduced metal species and Li.sub.2 O which may be recycled to the high temperature electrolytic cell.
2. Description of the Prior Art
Analysis of lunar soils and rocks collected during the Apollo program has demonstrated the presence of pyroxene type minerals (iron magnesium calcium silicates), plagioclase feldspars (calcium aluminum silicates), ilmenite (iron titanium oxides), and iron-nickel alloys. Based upon examination of the random samples returned to Earth during the Apollo program, the principal elements contained in such lunar "ores" appear to be oxygen, silicon, aluminum, calcium, iron, magnesium, titanium and nickel.
Some researchers have suggested that oxygen gas may be extracted from ilmenite (FeTiO.sub.3) via an initial chemical reduction using hydrogen transported from Earth as a reducing agent. Other researchers have proposed carbothermic reduction of lunar metal ores to separate the desired metal species.
Characterization of the high temperature electrochemistry of simulated lunar materials has been performed using metal silicate melts and platinum electrodes. High temperature electrolysis of metal silicates results in the simultaneous evolution of oxygen gas at the anode and deposition of a reduced metal silicon alloy slag at the cathode. Although the potential for using high temperature molten salt electrochemical techniques to separate oxygen gas and reduced metal species from simulated lunar materials comprising alkali oxides has been demonstrated, several technical limitations have been encountered. High temperature molten salt cells operating at temperatures in excess of about 1300.degree. C. experience chemical and electrochemical materials degradation which limits the cell efficiency and overall cell lifetime. Oxygen generated at the anode of a molten silicate (CaMgSi.sub.2 O.sub.6 containing Fe.sup.3+, Co.sup.2+, or Ni.sup.2+) electrolytic cell has a tendency to become trapped within the molten salt electrolyte, creating a foam in the proximity of the anode. This not only prevents efficient removal of oxygen gas from the cell, but it renders the oxygen gas more susceptible to electrochemical reduction at the cathode. Deposition of the reduced metal or metal silicate species at the cathode may result in dendrite formation and eventually produce inter-electrode short circuiting of the cell. Furthermore, continuous removal of reduced solid metallic species from the cathode is not practical in known cells, and the process would be limited to a batch-type operation.